C-H O hydrogen bond

The formyl C-H O hydrogen bond idea (Fig. 1.4) was first conceived for the catalyst 9 and its existence is supported by several X-ray studies of BX3 aldehyde... 

The crown-ether adduct shown in Scheme 13 exhibits both inter- and intramolecular C—H O hydrogen bonding in the solid state (Figure 3)7 ... 

Two molecules with comparable geometry in an asymmetric unit were found for 3,4-bis(4-fluorophenyl)-l,2,5-oxadiazole 2-oxide. The bond length of the dipolar N-O bond is 1.107 (7) A <2006AXEo4827>. In the molecule of 5-(6,7-dimethoxy-l,2,3,4-tetrahydroisoquinolin-2-yl)-4-phenyl-l,2,5-oxadiazole Ar-oxide, the six-membered heterocyclic ring has a flattened boat form. Intermolecular C-H- O hydrogen bonds link the molecules into dimers, which may be effective in the stabilization of the crystal structure <2006AXEo3130>. 

Figure B. Pictorial representation of the self-assembly of pseudorotaxa-nes based on (a) charge-transfer and C-H—O hydrogen-bonding interactions between 1,1 -diben-zyl-4,4 -bipyridinium dication and 1,5-dinaphtho[38] crown-10 (1/5DN38C10), and (b) hydrogen-bonding interactions between dibenzyl ammonium ion and dibenzo[24]crown-8 (DB24C8). A possible route towards the synthesis of rotaxanes and catenanes is also schematized.

The repeated occurrence of the otherwise rare catemer VII in the family of cubanecarboxylic acids under study here is quite likely the result of fortification of the catemer by the C-H—O hydrogen bond formed by the acidic cubyl C-H group.1261 This... 

Here, the theophylline molecules form hydrogen-bonded networks composed of one N-H N hydrogen bond and two bifurcated C-H O hydrogen bonds. 

V. Venkatesan, A. Fujii, T. Ebata, and N. Mikami, Infrared and ab initio studies on 1,2,4,5 tetrafluorobenzene clusters with methanol and 2,2,2 trifluoroethanol Presence and absence of an aromatic C H O hydrogen bond. J. Phys. Chem. A 109, 915 921 (2005). 

Furthermore, C-H - - O hydrogen bonds are formed between some of the polyether oxygen atoms and the a-bipyridinium protons. A second type of hydrogen bonding interaction, C-H- -77, is observed between the 1,4-dioxybenzene protons and thep-phenylene spacers. In most systems it is very difficult to measure their individual strength and importance in the assembly process. However, it is usually assumed that rr-stacking between complementary aromatic species is the main supramolecular interaction in these systems. 

Houk, Stoddart and Williams have carried out a detailed investigation (involving experimental and theoretical studies) to quantify the strength of C-H- -O hydrogen bonds in the formation of catenanes [82]. While the formation of the [3]catenane 67 was successful, its conversion to the [4]catenane 68 could not be achieved (see Scheme 32). 

Another instance of C—H- O hydrogen bond yielding a supramolecular assembly (at least in the solid state) is from complexes 82 and 83 between 1,3,5-trinitrobenzene and dibenzylideneacetone or 2,5-dibenzylidenecyclopentanone, respectively, which were investigated by X-ray diffraction199. C—H- O hydrogen bonds (such as those of 82 and 83) are three to five times weaker than N—H- O (and O—H- O) bonds200. 

Substituent effects on the endocyclic cleavage of glycosides by trimethylaluminium have been explained in terms of a cyclic C-H O hydrogen-bonded intermediate. ... 

The X-ray crystal structures (Figure 7) of 6-[Diquat] and 9-[Paraquat] demonstrate that complex formation is aided not only by [C—H O] hydrogen bonding and [N O] electrostatic interactions but also by charge transfer stabilization between the ir electron rich aromatic rings in the molecular receptors and the ir electron deficient bipyridinium rings in the substrates. 

For 23, both hydroxyl groups in the cis- and /ra t-isomer act as donors in intermolecular two-center and three-center O-H O hydrogen bonding, which may be classified as medium strong and weak. Additionally, there are C-H O hydrogen-bonding interactions in each crystal that in the ftf-isomer is intramolecular <2003JST(647)223>. 

Their research has focused on examining the effect of substitution on the aromatic ring in the crystal state. Their results show that different substitution leads to different structures being formed in the crystal state. They conclude that even weak intermolecular interactions such as C-H-O hydrogen bonds can be used to control crystal packing within glycoluril systems. 

During the course of a study of the salts formed by saccharin with quinine, haloperidol, mirtazapine, pseudoephedrine, lamivudine, risperidone, sertraline, venlafaxine, zolpidem, and amlodipine, a 1 1 cocrystal of saccharin and piroxicam was detected [68]. In the crystal structure, the asymmetric unit was found to consist of one saccharin molecule and one zwitterionic piroxicam molecule that were linked by two sets of N—H O hydrogen bonds. The piroxicam-saccharin synthons were in turn linked through bridging C—H O hydrogen bonds. Interestingly, the drug substance solubility out of the cocrystal was found to be comparable to that of the marketed piroxicam product. 

Section C Thomas, P.J., Qu, B.H. and Pederson, P.L. (1995) Defective protein folding as a basis of human disease. Trends Biochem. Sci. 20, 456-459. Wahl, M.C. and Sundaralingam, M. (1997) C-H...O hydrogen bonding in biology. Trends Biochem. Sci. 22, 97-102. Hampton, R., Dimster-Denk, D. and Rine, J. (1996) The biology of HMG-CoA reductase the pros of contra-regulation. Trends Biochem. Sci. 21, 140-145. Kantrowitz, E.R. and Lipscomb, W.N. (1990) Escherichia coli aspartate trans-carbamoylase the molecular basis for a concerted allosteric transition. Trends Biochem. Sci. 15, 53-59. 

---